The present invention relates in general to a hydraulic motor unit for use as a power drive source for a machine or a running vehicle. A variety of vehicles or machines are driven hydraulically by using a hydraulic motor unit, the most common applications being industrial vehicles of crawler type, or of wheel type such as a tractor, a bulldozer, a power shovel, etc., or hydraulically actuated winches to be installed on such industrial vehicles.
Such industrial vehicles as referred to above are generally adapted to heavy off-road use in irregular and rough areas, for example, in hilly areas or where there are many rocks or stones or greasy or slippery mud. To cope with such bad and irregular ground conditions, such industrial vehicles are generally crawler type or special heavy-duty tired wheel type. Under such conditions, these vehicles may occasionally encounter such obstacles on the ground during their services.
Such industrial vehicles generally use hydraulically actuated working members by way of such as a hydraulic actuator or cylinder unit for the purpose of operating a power shovel device or grading board in their field service, so such vehicles usually require a hydraulic energy or pressure source. In this respect, it is so convenient in practice to install a hydraulic motor unit for use as a power drive source. Since such a hydraulic motor unit is especially effective and suitable for a turning or steering operation of the vehicle by way of individually stopping either side of the endless crawler tracks which are generally arranged on both sides of the vehicle, or by driving both of such endless tracks in opposite directions, it is particularly advantageous to use such a hydraulic motor unit as a power drive source for such industrial vehicles.
When a hydraulic motor unit is used as a drive source in such industrial vehicles, should the hydraulic motor unit collide against an obstacle on the ground during operation, it may damage such hydraulic motor unit thus resulting in a breakdown. Therefore, it is preferable to design the whole hydraulic motor unit comprising such components as a hydraulic motor, reduction gears, braking mechanism, etc. so that the whole hydraulic motor unit may be included within the lateral dimensions of the crawler, so that it may not protrude therefrom, thereby reducing the risk of colliding with obstacles on the ground during operation.
As a running drive source of such vehicles, a hydraulic motor unit of axial plunger or piston type is generally advantageous in view of its generally high operating efficiency, or other advantageous operating properties. There are many applications using a hydraulic motor unit wherein various hydraulic motors including a reciprocating piston type are applied. For example, Japanese Patent Public Disclosure No. 108470/1974 discloses a radial piston type hydraulic motor unit and Japanese Utility Model Public Disclosure No. 82632/1977 discloses a hydraulic motor of swash-plate type axial piston pump. Among the plunger or piston type hydraulic motors, there is known that bent axis type hydraulic motor. There is shown the following table in Page 469 or "Yuatsu-Kuuatsu Binran" (Hydraulic-Pneumatic Pressure Technologies Handbook) which was compiled by the Japanese Institute of Hydraulic-Pneumatic pressure Technologies, and published Ohm, Inc., Tokyo Japan.
According to Table 1, it is appreciated that the bent axis type hydraulic motor exhibits the highest efficiency. In the case of the bent axis type hydraulic motor construction, it is obvious that the axis of the driving output shaft is not straight or is not aligned with the axis of the cylinder block which is adapted to drive the output shaft, and therefore, it is essential to arrange the cylinder block portion outside or beyond the span between the bearings which support the appropriate positions of the driving shaft. Therefore, it has been particularly difficult to design a hydraulic motor unit employing a bent axis type hydraulic motor which is compact in the longitudinal dimension. However, such compactness is important in the crawler driving hydraulic motor unit where there is a limit in the longitudinal or output (driving) shaft extension direction of the vehicle. In both of the above stated Japanese Patent and U.M. Public Disclosures, the axes are in aligned relationship with each other, and the piston block may be positioned between the shaft bearings, thus bringing the advantage that the resulting axial dimension may be made relatively short, thus bringing the longitudinal length within the desired limits.
In consideration of the advantageous features of the bent axis type hydraulic motor unit, it is is practicable to have it made short enough to be installable within the limits of a crawler construction, how advantageous it would be. The present invention is essentially directed to this end with the intention to employ a bent axis type axial piston motor having a high operating efficiency.
TABLE I __________________________________________________________________________ Displacement Max. Pressure max. efficiency Type [cm.sup.3 /rev] [Kg.function./cm.sup.2 ] max. r.p.m. [%.] __________________________________________________________________________ Rotary Type Gear Motor External 4-500 90-210 900-3500 65-85 Gear Type Internal 7-560 70-210 1800-7500 60-80 Gear Type Vane Motor Ordinary 10-220 35-70 1200-2200 65-80 of Balanc- Vane Type ing Type Special 25-300 140-175 1800-3000 75-85 Vane Type Reciprocating Axial Bent Axis 5-920 210-400 1000-6000 88-95 Type Piston Type Motor Swash Plate 4-500 210-400 1200-4000 85-92 Type Radial Eccentric 6-500 140-250 1000-1500 85-92 Piston Type Motor __________________________________________________________________________